From the corresponding wikipedia article:
The Famous 1938 Carnegie Hall Jazz Concert by Benny Goodman, Columbia Records catalogue item SL-160, was first issued in 1950. It was one of the first records of Benny Goodman music issued on the new long-playing format, and one of the first to sell over a million copies. A landmark recording, it was the premiere performance given by a jazz orchestra in the famed Carnegie Hall in New York City. It is the first ever double album. This album was also sold in a set of nine 45 rpm records in the same year by Columbia.